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The mkiv Supra Owners Club

OZ Wheels & Unsprung Weight


GavinL
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Hi....

 

In the absense of any cheap 17" wheels I have been investigating buying

a set of OZ wheels, namely the Superleggera 17" or 18" and resigning the

stock items to track days.

 

Firstly, does anyone know of a supplier of these wheels in the UK.

 

Secondly, the wheels are considerably lighter (about 8-10 pounds)lighter

than the stock wheels thus reducing the unsprung weight of the car and

from what I have read on the Net this appears to be desirable. Any suspension/handling

experts out there care to comment

 

 

TIA

 

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Reducing unsprung weight is a bit of a holy grail for sports and racing cars.    Unpsrung weight is literally that - wheels / tyres / brakes / hubs etc.   all the bits attached to the hubs that are not supported by the suspension springs.

 

If the unsprung weight is as light as possible, this lets the wheels do what they're supposed to do which is to stay in firm contact with the ground as much as possible.

Imagine if you had a wheel rim that was made of lead (i.e. v. heavy) and it hit a big bump at speed.   The spring would compress massivley due to the huge weight of the wheel and the wheel would take longer to resume full contact with the road surface.

It's like if you hold a dumb-bell out at arms length and try to move that dumb-bell's direction QUICKLY.   v.v.hard as it's so heavy.     so the lighter the parts of the car that are "unsprung"  (wheels / tyres / brakes / hub) the better the springs and dampers can control the wheels etc.

The other effect that a heavier wheel hasis that it has a large rotational moment of inertia, which basically means that it is hard to increase and decrease the rpm of that wheel.     i.e. i becomes harder to rotationally accelerate and de-celerate that wheel which simply means that the car won't accelerate as quickly or decelerate (brake) as quickly.

 

Top racing cars (& even exotic road cars) will have wheels made of magnesium as it's very low density stuff but still sufficiently strong not to buckle under the forces.

 

I think even racing bicycles have magnesium wheels but it costs literally thousands of pounds.

 

 

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